The present invention relates to a flow meter and more particularly to a process gravity free fall flow meter for measuring the flow rate and accumulated weight of solid powdered, particulate or granulated materials or other solids of like nature such as seeds, grains and pellets passing through a measuring chamber.
The current state of the art in the area of the continuous measurement of flow rates and accumulated weights of solid particulate materials is limited primarily to four systems: Coriolis force flow meters, impact flow meters, flow meters based on electronic load cells, and turbine flow meters.
Of the four major classes of flow meters suitable for solid particulate materials, each can be found to have its limitations, the major examples of which can be related to the physical phenomena and forces involved in the principles of their functioning and in the complexity of mechanisms necessary for adequately controlling and compensating for the related problems and deficiencies.
As is well known to those practiced in the art, a Coriolis flow meter is a mass flow meter that measures the mass flow rate of material flowing in a flow tube supported at both ends by oscillating the flow tube and detecting a Coriolis force acting on the flow tube, said measured force being theoretically proportional to the mass flow rate of the material. The Coriolis force is detected as a difference of phases produced at symmetrical positions between the supporting points and the center portion of,the flow tube when the flow tube is driven alternately at its center portion in a direction perpendicular to the supporting axis.
In operation, the flow tube is electromechanically vibrated out-of-phase with respect to a balance tube which is provided to reduce the vibrations that would be associated with a single unbalanced flow tube. These vibrations impart a Coriolis acceleration to material flowing through the flow tube. The reaction force to this Coriolis acceleration results in a slight distortion of the vibration mode shape of the flow tube. This distortion is measured by sensors connected to, or associated with, the flow tube. The sensors may be either of the velocity or displacement type. The material flow rate is proportional to the time or phase delay between the signals generated by two such sensors positioned along the length of the straight flow tube. A single sensor may also be used. Output signals of the sensors are applied to electronic apparatus which derives the desired information, such as mass flow rate, for the material in the flow tube.
Among the problems encountered in the application of the Coriolis force for the accurate measurement of the flow rate of a material are those related to correcting errors caused by a differences in or changes in the density of the flowing material, differences in the temperature deformation of the materials comprising the flow tube, and differences in temperature in the flow tube and the resonant member. Other difficulties related to the practical functioning of Coriolis force flow meters will be apparent to those practiced in the art. The measures required to circumvent and overcome the various limitations of the Coriolis force-based systems tend to greatly increase the complexity, and therefore the cost, of such systems.
The impact flow meter is widely employed in industry due to its potential robustness and ease of insertion into flow systems. The systems are based on the measurement of one component (usually horizontal) of the force of impact imparted by the flowing material as it falls on an impact plate positioned in the general line of flow of the material of interest. The impact of the flowing material on the impact plate produces a minimal movement or distortion in the position of the plate. A sensor, force transducer or other mechanism transfers the limited movement or distortion of the impact plate to the appropriate sensing device and related electronic circuitry which then converts that signal to an instantaneous mass flow rate based on suitable calibration data.
While the theory of the impact mechanism is clear, in practice, there are several problems that can significantly affect the accuracy of the force measurement and, therefore, the calculated flow rate. Simple physics shows that the force imparted to the impact plate by falling material will be a direct function of the relative angle of impact on the plate. Any change in that impact angle produced by an improper installation of the device in the flow path or subsequent movement after installation will introduce significant errors in the calculation of the final flow rate. In addition, because the movement of the impact plate is very limited, the mechanism employed to sense and transmit the resultant impact force to the corresponding electronic circuits must by necessity be very sensitive. That sensitivity necessitates the use of measures to protect the sensing mechanism and/or correct for changes in the response of said device, all of which imply the need for more complexity and cost in the construction and operation of such devices.
In a typical configuration for such units, bulk material is allowed to fall from a defined height upon a deflector plate which has been arranged at an angle to the vertical, with the flexural moment generated in the process being determined within the flexible joint of the deflector plate. The deflector plate arrangements have certain defects which result in relatively severe inaccuracies in measurement in the case of one and the same bulk material and which make problematical use of the same unit for a variety of materials, such as in dosing processes. Because in most such units moments are measured, it is not only the impact force which is generated via changes in pulsing which is decisive, but also the specific location where the bulk material impacts the deflector plate. In this instance, considerable variations are possible, depending upon the nature of the material involved. Furthermore, the type of momentum transmission involved is essentialxe2x80x94the degree of force transmitted is greater in the case of elastic impact than with inelastic impact. The specific impact rate, which must be taken into consideration, also varies with the type of bulk material involved and the condition of the bulk material at a given moment. The units described generally provide satisfactory results with respect to the bulk material to be weighed only through extensive calibration and generally require frequent control of such calibration.
Devices based on electronic load cells are also common in industry due to their theoretical precision and adaptability to transport belts and related systems as well as direct static weighing. Electronic load cells devices, however, are found to be extremely sensitive to physical abuse, requiring frequent calibration and control to maintain accuracy and precision. In addition, they are relatively delicate and easily broken by misuse. Their accuracy is also dependent on their proper installation so that any dislocation or movement in their location can produce significant errors in the final result.
Turbine flow meter devices have found great application in the measurement of fluid flows, especially in pressurized gas flow measurements and in simple pumped liquids such as is found in gasoline pumps. In such applications, however, the fluid flow is generally relatively constant and there exists a natural resistance in the flow field that prevents any xe2x80x9cfree wheelingxe2x80x9d of the measuring turbine when the force of the flowing material changes. In free flowing systems such as those contemplated by the present invention, turbine flow meters are rare and those in existence must incorporate some braking mechanism to prevent xe2x80x9cfree wheelingxe2x80x9d of the turbine, since free fall systems will not have the natural braking mechanism present in a pumped fluid system. Such braking mechanisms routinely involve some mechanical and/or electromagnetic phenomenon that requires continual or periodic monitoring of the applied braking force to insure constancy of its action so as not to over compensate and thereby alter the resultant forces and introduce measurement errors, or to detect and compensate for variations in braking force due to wear, fatigue or changes in characteristics due to changes in temperature or other ambient conditions.
As will be seen by the following disclosure, most of the complications and disadvantages of the flow measuring systems currently known to the art can be simplified, overcome or avoided completely by the present invention.
In view of the foregoing description of the current related art, it is an object of the present invention to provide a process mass flow apparatus for measuring the mass flow rate of a powdered, granulated or otherwise substantially divided process solids, seeds, grains, or similar particulate materials comprising: a process material inlet, a process material outlet, a flow passage or measuring chamber connecting the process material inlet and the process material outlet, a process material flow sensor located in the measuring chamber which provides a raw output signal corresponding to an unknown mass flow rate, and a signal processor, computer, programmed logic controller (plc) or other device of a similar function known to the art which contains an empirically derived conversion function for converting the raw output signal to an adjusted-signal indicating the mass flow rate of the process material. An additional object of the invention is to provide a method for determining an unknown mass flow rate using an empirically derived conversion function, the function being derived by correlating the raw output signal of a mass flow apparatus sensing the flow of a calibration material with the output signal of the mass flow instrument sensing the flow of the process material and a method for calculating the accumulated weight of material having passed through the measuring chamber during a period of time specified by the user. The exemplary mass flow instrument may further include a flow control portion, which may comprise a control unit, a valve drive, a valve, or other control or warning device known in the art that responds to an electronic, visual, audio, or other signal form produced by said control unit as a result of the process of determining the flow rate and/or accumulate weight of process material passing through or having passed through the measuring chamber.
In accordance with another embodiment of the present invention, a method for determining an unknown mass flow rate of a process material flowing through a process mass flow apparatus is provided. The process mass flow instrument provides a raw output signal corresponding to mass flow of the process material through the process mass flow apparatus. The method comprises the acts of providing one or more calibration materials which may or may not be the same as the process material and providing a mass flow apparatus similar to the process mass flow apparatus which is used for calibration purposes. The calibration mass flow apparatus is calibrated using the calibration material or materials by allowing said calibration material or materials to flow through the calibration mass flow apparatus at various known mass flow rates and correlating the raw output signal with the corresponding known flow rate and subsequently deriving a flow rate conversion function by applications of mathematical regression analysis using procedures or computer programs well known in the art. The conversion function may be a linear, quadratic, or cubic polynomial function or other mathematical function suitable for the specific application. Included in the conversion function is a multiplication factor or final calibration factor that allows the user to fine-tune the characteristics between the process mass flow meter and the calibration mass flow meter. After the calibration function is determined it is programmed into the control unit of the process mass flow meter. Once the process mass flow meter is installed in its final position, a final calibration is carried out by passing process material through the mass flow apparatus at a known flow rate. The ratio between the known flow rate of process material and that indicated by the preliminary calibration, hereafter called the final process calibration factor, K, given by the ratio of the known process material flow rate, F2, to the indicated flow rate, F1, (K=F2/F1) is then employed as the final calibration factor which is entered into the control unit program by the user to complete the calibration process.
A typical calibration function for a preferred embodiment of the present invention would be of the form
Q=K*[(A*S3)+(B*S2)+(C*S)+D]
where Q is the flow rate of process or calibration material passing through the measuring chamber at the instant of signal conversion, K is the previously defined final process calibration factor, S is the value of the raw signal produced by the material flow passing through the measuring chamber, and A, B, C, and D are the derived coefficients for a polynomial regression best fit curve to the calibration data.
Another object of the present invention is to provide a means by which the user can carry out in a continuous way a control of the flow rate and accumulated weight of a granulated, powdered or other particulate material as it passes through the zone of measurement in a way that produces an appropriate signal allowing the calculation of flow rate and/or accumulated weight of material passed as well as offering the possibility of providing a signal that may subsequently be employed in the control of one or more related processes such as process feed, valves, motors, etc. The fact that the user can pass materials as diverse as grains, seeds, pellets, powders, etc., in a continuous way makes much more efficient diverse processes such as loading, transport, transfer, packaging, and the like. In addition, the present invention provides the ability to measure and control flow rates and accumulated weights of materials in fixed lines of transport, in dosing operations, for fiscal control operations, and in situations requiring portable operation all with a simple, easy to use apparatus.
The apparatus of the invention has a measuring chamber having a body comprising a flow tube or conduit having a rectangular, circular, elliptical, or other cross section through which the Solid material to be measured is directed. Within the measuring chamber is located a movable element with a fixed axis of rotation on which the passing solid material exercises a force or torque proportional to the mass flow rate of the solid material and acting against a constant restoring force applied to the axis or the movable lever device, said restoring force being such that the degree of rotational or linear movement imparted by the passing solid will be a function of the force imparted by the solid material due to gravitational forces in free fall or to momentum imparted to said process material by some mechanical means of material transport.
Attached to the axis of the movable lever assembly or to some other convenient part of said assembly is a digital or analog device that measures the angle of rotation of said movable element or some proportional value of the linear movement of said assembly. The raw signal from the digital or analog measuring device is passed to an appropriate electronic circuit that conditions the raw signal in a manner such that a properly programmed associated microprocessor, computer, programmable logic controller (plc) or other similar device receiving said signal converts said signal to an instantaneous flow rate based on a preprogrammed calibration function or table. An additional step in the program then employs an internal clock or other suitable device or method and the previously calculated instantaneous flow rate for calculating the accumulated weight of material having passed through the measuring chamber during the measuring process. If so desired, the raw signal and/or calculated flow rate or accumulated weight can be employed as a feedback signal for the control of appropriate valves, motors or other control devices as are well known in the art.
A particularly important embodiment of the invention is its applicability as a portable device for measuring and controlling the amount of solid material being extracted from or loaded into tanks, trucks, rail cars, ships or other containers or transport systems in a continuous manner, providing important information related to the rate of material transfer, partial weights of material transferred, and final total weights transferred from or to the point of interest to the user. In particular, an important embodiment of the present invention is its application in mobile field operations such as, for example, the loading of seeds, grains, or other bulk materials into trucks, rail cars, silos, etc., at the time of harvest, storage, or production.
A second important embodiment of the invention is its use in fixed process lines for which its compact design and potential for structural modification and custom design make it a particularly attractive alternative to similar products known in the art.
The invention described is notable for its ease of use and flexibility of installation, requiring no more than correct leveling and a simple in-place calibration process. Other factors related to the installation of the invention vary according to the place and form of use.